(1) Field of the Invention
The present invention relates generally to transducers, and more particularly to slotted cylinder transducers having a cylindrical piezoelectric driver element bonded to the inside of a cylindrical shell and having a slot cut along the length of the shell and the driver element.
(2) Description of the Prior Art
Transducers are used in the generation and reception of underwater sound. A typical configuration of a slotted cylinder transducer would have the acoustically active component, or electromechanical driver, located in the interior cavity of a cylindrical shell. The shell would be fabricated of a metal or a laminated composite material. The driver is commonly a cylinder or set of rings of piezoelectric material that is mechanically connected to the cylindrical shell by means of an epoxy bond between the outer surface of the driver and the inner surface of the shell. The driver rings, or cylinder, are frequently constructed of an assembly of segmented pieces which are cemented together and electrically connected via foil electrodes located in the joints between adjacent segments. The curvature of the cylindrical shell places a residual compressive stress on the driver. This compressive stress on the driver must be maintained to prevent the driver from undergoing tensile strain which would cause the piezoelectric driver material to fracture. The driver receives additional compressive stress from increased hydrostatic pressure as the transducer is used in underwater operations.
A slot extending the length of the cylinder and parallel with the cylindrical axis is cut through the wall of the shell and also through the driver. Inserts or end shanks are bonded to the interior surface of the shell adjacent slot and to the ends of the piezoelectric element. When the driver is excited with an alternating electrical signal, the circumference of the driver will expand and contract against the inserts, creating flexural vibration in the cylindrical shell. The fundamental mode of this vibration consists of a nodal region of minimal or no radial displacement, located 180.degree. from the slot. In this mode, the radial displacement of the cylindrical shell increases in magnitude from a minimum in the nodal region to a maximum near the slot. The motion of the shell can be likened to a conventional tuning fork whose tines have been bent into a circular shape. The radial displacement of the cylindrical shell radiates acoustic energy into the medium surrounding the transducer. The transducer can also be used as a hydrophone by detecting acoustic vibrations in the medium that excite mechanical vibrations in the cylindrical shell, which in turn generate an electrical signal in the driver material.
To increase the level of acoustic energy radiated by the transducer, the wall thickness of the cylindrical shell can be tapered having its thickest point at the nodal region and becoming progressively thinner towards the slot. Such a tapered shell is disclosed in U.S. Pat. No. 4,774,427 to Plambeck. Some transducer applications, such as those requiring the acoustic signal to travel long distances, require further increases in radiated energy. Additionally, increased detection capabilities are required for transducers used as hydrophones to receive such long distance signals.